The invention concerns a method for testing the functionality of a spectrometer for faults and a spectrometer with fault detection device.
Optical spectrometers of simple construction are being used increasingly in various fields and areas of technology, thus for example in the automobile sphere or in application for sorting articles. One of the main problems of such optical spectrometers is monitoring the long-term stability of the system. Thus, firstly the state of the primary light source and the transmission or degree of soiling of the spectrometer must be monitored and secondly the spectral calibration of the system must be ensured. But the current state of the art has so far provided no options, or only elaborate ones, for validating the optical specifications of a spectrometer as a whole, and enables only limited electronic testing of the individual components. Also the usual subsequent referencing of the spectrometer with a sample or the like does not by any means guarantee functioning of the system, for example in the case of damaged filters.
It is therefore the object of the invention to provide a method for testing the functionality of a spectrometer and a spectrometer, with which it is possible to monitor the long-term stability of the spectrometer even if the spectrometer is not directly accessible.
This object is achieved according to the invention by the characterising features of the main claim and ancillary claim in combination with their introductory parts.
An essential concept of the invention lies in variably adjusting the colour temperature of a radiation source and, on the basis of the known Planck radiation curve which with a very good approximation also applies to the radiation source used, to infer the optical characteristics of the spectrometer. Due to the known emission values of the radiation source at different colour temperatures, it is possible to develop a suitably large data space for fully optically testing the spectrometer. Here the known emission values used as reference values can be determined by a parallel spectrometer with N wavelength channels for example at two colour temperatures of the radiation source, yielding the resulting 2N-dimensional data space for testing the spectrometer. For the process of long-term monitoring there may be provided a secondary radiation source which is arranged on the receiver side, that is, behind the object to be transmitted or reflected and which is adjustable to freely selectable colour temperatures. But the colour temperature of the primary radiation source can also be traversed, but in this case care must be taken that the optical path contains no variable parameters, such as for example objects with varying material properties or characteristic photometric factors. This can be avoided by a reference material, for example Teflon.
With the invention, a test of the following spectrometer parameters can be performed:
1. The total transmission of the spectrometer can be detected through the intensity of the individual channels (monitoring for fibre breaks, lens scratches, power failure of the electronic amplifier unit, failure of the primary radiation source or secondary radiation source);
2. the individual transmission of the different filters or detectors is tested through the individual intensity of the various channels (monitoring of the individual filter transmissions and integral spectral sensitivity of the individual detectors or their total failure);
3. the individual spectral characteristics of the optical components can be monitored on the basis of the deviation of a single channel from the nominal value when the other channels have constant values (monitoring of colour centre formation of the fibre, absorption of the lens, wavelength shift of the individual filters);
4. the integral spectral characteristics serve as self-monitoring of the secondary radiation source (monitoring of the colour temperature in case of a constant lamp current with reference value fixed beforehand).
On account of fault detection, in case of minor deviations an internal recalibration of the spectrometer can be performed, otherwise in case of major faults an exact fault message or diagnosis can be outputted, so that any repair is made substantially easier.
The invention offers a reliable diagnostic unit without major expenditure on maintenance for long-term operation of a spectrometer, for example in the automobile sphere, without which unit it is not possible to use the spectrometer.
Due to the measures provided in the subsidiary claims, advantageous developments and improvements are possible.